ON EUDIOMETERS. 293 



eudiometer. At the top of the eudiometer is a capillary 

 tube provided with an iron stop-cock and joint, to which a 

 laboratory tube can be attached. The eudiometer and the 

 lower part of the other tube (which is open at the top) are 

 surrounded by a glass cylinder filled with water. The tem- 

 perature being maintained constant by the water, the gas is 

 measured in the eudiometer, which is provided with plati- 

 num wires to which copper wires can be attached, and an 

 explosion can be made in the tube below the water, and 

 readings can be taken off at once. The gases are introduced 

 by means of a laboratory tube, as it is termed, which is 

 placed in a mercurial trough, which may be raised or 

 lowered by means of rack- work. 



The difference of level of the mercury in the eudiometer, 

 and second or pressure tube, will give very simply the 

 height of the column supported by the gas, and this has 

 to be introduced into the barometric calculation. The 

 temperature is obtained by a thermometer standing in the 

 water by the side of the eudiometer. The substance for 

 absorption to be used will depend on the gas to be 

 absorbed, but it is always used in the liquid condition. 

 Whilst the gas remains in the measuring tube, a few 

 drops of the liquid reagent are introduced into the 

 laboratory tube by a bent pipette. The gas is then 

 allowed to pass once more into the laboratory tube. The 

 mercury is depressed, and the whole of the side of the 

 vessel becomes moistened with the liquid, and presents 

 a large surface for the absorption of gas which takes 

 place very quickly. Let me by way of contrast show yau 

 the absorption of carbonic anhydride by liquid potassic 

 hydrate. I take a small bent pipette with an india- 

 rubber connector, and so introduce a little into the gas, 

 and agitate slightly so as to moisten the side of the tube. 

 You will see the carbonic anhydride very rapidly absorbed 

 by the solution, whereas the former experiment, which has 

 been standing now nearly an hour, is not yet .complete. 

 You see therefore the great advantage of the liquid reagent 

 in the apparatus of Regnault and Keiset. This apparatus 

 was afterwards very much improved by Dr. Frankland and 

 Mr. Ward, who added to it as it now stands a barometer. 

 You will see that as originally made this instrument 

 would have to have all the barometric corrections made as 



